1. Field of the Invention
The present invention relates to communications systems, and more particularly, to channel estimation in communications systems.
2. Description of the Related Art
In a typical digital communications system, the channel is bandlimited and disperses a signal passing through the channel. When the channel bandwidth is greater than the bandwidth of the signal, signal spreading is negligible. However, when the channel bandwidth is close to the signal bandwidth, signal spreading can exceed a symbol duration and results in intersymbol interference, i.e., overlapping of symbols, which interferes with the detection process at the receiver and degrades system performance (e.g., increases system error rates). Unlike other forms of noise, intersymbol interference cannot be remedied by increasing transmit signal power. Since the frequency response of the channel is typically not known with sufficient precision to allow for a receiver design that will compensate for intersymbol interference for all time, a filter (i.e., an equalization filter) corrects the channel-induced distortion at the receiver using parameters that are adjusted based on estimates of channel characteristics.